The Ten Books on Architecture, 10.14

Vitruvius  translated by Joseph Gwilt

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Of the Tortoise for Filling Ditches

14The tortoise contrived for filling up ditches, which also affords an access to the walls, is thus made. A base, called by the Greeks εσχάρα, is prepared twenty-five feet square, with four cross pieces. These are tied in by two other pieces, one twelfth high, and one half wide, distant from each other about a foot and a half, and under each of their intervals are placed the naves of wheels, called in Greek ἁμαξόποδες, within which the axles of the wheels turn in iron hoops. The naves are so made that they have holes in their heads, in which the handspikes being received, are made to turn them. The naves thus revolving, it may be moved forward or backward, to the right or left, or diagonally, as wanted.

2Above the base are placed two beams, projecting six feet on each side; round the projections of which two other beams are fixed in front, seven feet long, and their width and thickness as described for the base. Upon this frame which is to be morticed, posts are placed, nine feet high, exclusive of their tenons, one foot and a palm square, and a foot and a half distant from each other. These are tied in at top by means of morticed beams. Above these beams are braces, with tenons, the end of one being let into the next to the height of nine feet, and over the braces is a square piece of timber, by which they are connected.

3They also are kept together by side pieces, and are covered with planks of palm, in preference to other wood: if those are not to be procured, by other wood of a strong nature, pine and ash, however, excepted; for they are weak and easily ignited. About the planking are placed gratings, made of slender twigs recently cut, and closely interwoven; and then the whole machine is covered with raw hides, as fresh as can be procured, doubled and stuffed with seaweed or straw steeped in vinegar, in order that it may resist the strokes of the balistæ and the attacks of fire.

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